As the night rain fell on the veranda of the luxury villa, the Italian countess, clad only in a white robe to hide her faded beauty, stepped on to the wall guarding the cliff's edge. Her head swimming from a cocktail of whisky and sleeping pills and suffering from famously "weak nerves", she plunged to her death.

It sounds like the opening of a bad novel. But it has now been claimed that the accepted truth about the death of Countess Francesca Vacca Agusta in 2001 may indeed by a fiction. The brother of the fashion model-turned wealthy countess has now called for the case to be reopened, claiming that his sister didn't jump, she was pushed.

The gruesome mystery gripped Italy for months after the widow of the aristocratic helicopter tycoon Count Corradino Agusta, fell 80 metres to her death from the veranda of her villa in the millionaire's playground of Portofino, on Italy's north-west coast.

The inquiry at the time was told there were only three people in the house. Her lover, a Mexican called Tirso "Tito" Chazaro, her maid, Susanna Torretta, and a Polish domestic. The Countess supposedly fled from the house onto the veranda in a drunken rage, mounted a small wall at the edge of the veranda and, slipping on wet leaves, toppled over the edge.

But now the dead woman's brother, Domenico Vacca Graffagni, believes that Chazaro - the man revealed to be sole heir to her €26m (£18m) fortune, pushed her. He is demanding that the inquiry into his sister's death be reopened.

The ingredients of wealth, aristocracy and blood would be quite enough to sustain the average whodunnit, but in the case of Countess Agusta there was much more. Her marriage to Count Agusta broke down in 1985, though they were never divorced. She then took up with Maurizio Raggio, who happened to be in charge of the personal finances of Bettino Craxi.

Craxi, the prime minister during the 1980s, leader of the Socialist Party, patron to rising businessman Silvio Berlusconi, was the political boss at the centre, years later, of the so-called "Tangentopoli" ("Bribesville") corruption investigations that convulsed Italy in the early 1990s. Craxi fled to Tunisia where he died in exile and disgrace in 2000, convicted in absentia of corruption.

As the Tangentopoli scandal consumed practically all of Italy's established political parties, Countess Agusta and her well-connected lover, Mr Raggio, did not escape the investigators' attention. They alleged that the countess was the holder of Swiss bank accounts used by Craxi to launder some of the immense quantity of dirty money that came sloshing through his office. To avoid prison, in 1994 the countess and her lover fled to Mexico, but were extradited back to Italy.

Convicted of his role in the affair, Mr Raggio was sentenced to three years and four months in prison for money laundering and managing Craxi's dirty money. But by the time of her death, the Countess's affair with Mr Raggio was over and she was living with the Mexican who is now accused of involvement in her death.

Mr Graffagni told the Italian daily La Repubblica: "The inquiry was closed in a hasty fashion because of absence of proof, relying too readily on 'reasonable doubt'." He declined to preview the new evidence he intends to present to the inquiry, if it re-opens, but it is plain that the Mexican is the man in his sights. "It was manslaughter," he said. "He [Chazaro] was always beating her. He didn't mean to kill her. But that evening things didn't go the way the Carabinieri said, my sister was not drunk and she did not slip on wet leaves on the veranda."

Three weeks after her fall - Mr Graffagni claims she plunged not from the veranda but from a terrace on a different floor of the building - the countess's body washed up on the beach of Toulon, on the French Riviera. When the last of the many wills she apparently wrote was opened, the sole beneficiary was Mr Chazaro.

The will was challenged by Mr Raggio; in a secret out-of-court settlement, Mr Chazaro took 60 per cent and Mr Raggio - said to be the only man able to access some of the secret accounts where the countess had her money - took 40 per cent. Mr Chazaro was last heard from 12 months ago in Mexico.